1. Field of the Invention
The present invention relates to an induced magnetic field detecting apparatus and an induced magnetic field detecting method.
2. Related Art of the Invention
FIG. 10 is a block diagram showing an outline of the basic configuration of a most common conventional scanning laser SQUID microscope.
As shown in the same figure, this scanning laser SQUID microscope 200 is equipped with a laser generator 201 which generates laser light 202. The laser light 202 is subjected to intensity modulation using a laser modulation signal generated in synchronization with a predetermined reference signal 210, condensed by an optical system 204 and then irradiated onto a sample (inspection target) 205. When the condensed laser light 203 is irradiated onto the sample 205, a photoinduced current is generated in the sample 205 and magnetism 206 is induced by that current. The intensity of this magnetism 206 is detected by a SQUID magnetic sensor 207.
In this case, the position of the point of irradiation on the sample 205 of the condensed laser light 203 is configured to be immediately below the SQUID magnetic sensor 207 which is disposed on the opposite side relative to the position of the sample 205. This is the necessary condition so that the SQUID magnetic sensor 207 can accurately detect the magnetic field generated through the irradiation of the laser light.
The magnetic field intensity detected by the SQUID magnetic sensor 207 is inputted to a lock-in amplifier 209 as a magnetic field signal 208. The lock-in amplifier 209 adjusts the phase difference between the magnetic field signal 208 and the reference signal 210, extracts a component having the same frequency as that of the reference signal 210 from the magnetic field signal 208 and outputs the component as an intensity signal 212. A series of such signal acquisitions are performed on the sample 205 by scanning a stage on the XY plane and it is thereby possible to acquire an image of a magnetic field distribution in the sample, which can be used to detect defects such as breakage of a wire of an inspection target.
As an application of such a scanning laser SQUID microscope, applications for an inspection and analysis of an LSI are under study. For example, Japanese Patent Laid-Open No. 2002-313859 discloses a technology of inspecting a semiconductor chip in a wafer state and a mounted state using a scanning laser SQUID microscope. Furthermore, as shown in FIG. 11, for example, the same document discloses a laser light source 151, an optical system 153 to condense laser light, a laser beam 162, a semiconductor chip 170 onto which the laser beam 162 is irradiated, a SQUID magnetic fluxmeter 112, a control apparatus 156 which controls the whole apparatus, a fixing member 160 which fixes a relative positional relationship between the optical system 153 and the SQUID magnetic fluxmeter 112 and a display device 158 or the like (see, for example, FIG. 14 of Japanese Patent Laid-Open No. 2002-313859). This is a configuration different from that in FIG. 10 in that the optical system 153 and the SQUID magnetic fluxmeter 112 are disposed on the same side as the semiconductor chip 170 which is the inspection target.
Furthermore, a scanning SQUID microscope shown in FIG. 12(A) and FIG. 12(B) is proposed as another conventional technology in a configuration with an optical system and a SQUID magnetic fluxmeter disposed on the same side (for example, see FIG. 11 of Japanese Patent Laid-Open No. 2001-50934).
FIG. 12(B) discloses a case where a laser light irradiation position P and a SQUID 252 are disposed on the same side with respect to an inspection target W on a stage 310, with such a configuration that a heat insulating case 253 is formed like a hollow cylinder, three sets of a pickup coil 251 and the SQUID 252 are incorporated in the heat insulating case 253 and laser light from a laser light generation source 221 is introduced into an objective lens 227 along the central axis of the heat insulating case 253.
When the configuration shown in FIG. 10 is applied to a case where a semiconductor chip mounted on a board is inspected, the presence of the board may obstruct laser irradiation onto the semiconductor chip which is the inspection target. In such a case, the magnetic field itself is not generated from the semiconductor chip, which makes inspection impossible, while the configuration as shown in FIG. 11, with the optical system 153 and the SQUID magnetic fluxmeter 112 disposed on the same side of the semiconductor chip 170 which is the inspection target, has no influence of the board and is considered as the configuration which makes it possible to inspect not only a semiconductor chip before mounting but also a semiconductor chip after mounting. The same applies to the configuration in FIG. 12, too.
On the other hand, instead of the configuration of condensing laser light on a sample with an objective lens, a SQUID microscope apparatus which observes the surface of a sample using evanescent light is proposed (see Japanese Patent Laid-Open No. 2003-287522). This SQUID microscope apparatus has a configuration in which an end of an optical fiber which has been subjected to predetermined processing is brought close to a distance on the order of the wavelength (several hundreds of nm) of light from a sample and the sample is excited by evanescent light generated from the end. Because evanescent light is an evanescent wave (evanishing wave) and can only exist in a range on the order of the wavelength of light, it is clearly distinguished from laser light.
Therefore, the SQUID microscope apparatus using such a nature specific to evanescent light allows observation up to the depth on the order of several nm from the surface of the sample with high accuracy, whereas it is not possible to non-destructively inspect, for example, an inner circuit of a semiconductor chip having several hundreds of μm in thickness mounted on the board.